Advances in Nuclear Physics, Volume 22
Presenting five pedagogical articles spanning frontier developments in contemporary nuclear physics, this text ranges from the physics of a single nucleon to nucleosynthesis in the Big Bang.
TABLE OF CONTENTS Advances in Nuclear Physics, Volume 22
2: THE NUCLEAR PHYSICS INPUT
2 THE NUCLEAR PHYSICS INPUT
2.1 Rate Equations and Reaction Rates
As we have seen in the general introduction in Section 1, nuclear reactions play an essential role in the evolution of a star and in many other astrophysical scenarios. Obviously, they change the chemical composition of the environment in a manner that can be described by a set of rate equations,
where Y i is the relative abundance, by number, of the nuclide i. Alternatively, the rate equation can be expressed in terms of the mass fraction X i of a nuclide, which is related to the relative abundance via X i = A i X i where A i is the number of nucleons in the nuclide i. For a complete description of the astrophysical scenarios with which we are concerned in this chapter, the rate equations have to be supplemented by equations that, in the case of a star, describe energy and momentum conservation, energy transport, the state of matter, etc., or, in the early universe, the time evolution of the temperature.
The coefficients C in Eq. (2.1) are the rate constants. In the case of the destruction of the nuclide j, as in photodissociation ( ? + j ? i + y), the nuclide i will be generated and the coefficient C i j is positive. Similarly, the nuclide i can either be generated ( e ? + j ?
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